<template>
    <ul class="list">
        <li 
            class="item" 
            v-for='item of letters' 
            :key='item'
            :ref='item'
            @touchstart='handleTouchStart'
            @touchmove='handleTouchMove'
            @touchend='handleTouchEnd'
            @click='handleLetterClick'
        >{{item}}</li>
    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props:{
        cities: Object
    },
    computed: {
        letters(){
            const letters = []
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    data(){
        return {
            touchStatus: false,
            timer: null,
            startY: 0
        }
    },
    updated(){
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart(){
            this.touchStatus = true
        },
        handleTouchMove(e){
            if(this.touchStatus){
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - this.startY) / 20)
                    var len = this.letters.length
                    if(index >= 0 && index < len){
                        this.$emit('change', this.letters[index])
                    }
                },16)
            }
        },
        handleTouchEnd(){
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
    @import '~style/varibles.styl'
    .list
        display: flex
        flex-direction: column
        justify-content: center
        position: absolute
        top: 1.58rem
        bottom: 0
        right: 0
        width: .4rem
        .item
            text-align: center
            line-height: .4rem
            color: $bgColor

</style>